1. Field of the Invention
This invention relates to wide angle zoom objectives, and more particularly to two-component zoom objectives having a first lens component of negative power and a second lens component of positive power with the air separation therebetween variable to effect a change in the focal length of the entire system.
2. Description of the Prior Art
Up to now, a two-component zoom objective lens whose first component counting from the front is of negative power and whose second is of positive power as illustrated in FIG. 1, or a so-called inverted telephoto type, has represented a form of lens system offering a great advantage at an increase in the angular field. But, since the wide angle setting for the maximum possible angular field takes place when the first and second components I and II are most widely separated from each other, the diameter in the front members tends to increase as the maximum possible angular field increases. This tendency becomes prominent when a much-desired increase in the angular field is intended. With a lens system having such a wide angular field, when its bulk and size is reduced unduly, the barrel type distortion in the wide angle position increases so rapidly that correction thereof becomes very difficult to perform.
Conventionally, most wide angle two-component zoom objectives include, as the first lens L1 in the first component I, either a meniscus lens of negative power convex toward the front, or a meniscus lens of positive power convex toward the front. They contribute somewhat different advantages to their respective systems. It is generally known that, as stated in Japanese Laid Open Patent No. Sho 52-134452, the choice of the latter type is preferable to achieve good correction of distortion, and a minimization of the diameter of the front lens members is facilitated by employing the former type.
Examples of two-component wide angle zoom objectives are disclosed in U.S. Pat. Nos. 4,159,865 and 4,153,339.